Nutrients in Potting Soil
Nothing looks better on a summertime patio than containers of beautiful blooms pouring over the sides. Container gardeners understand the importance of a proper potting soil for best results. Commercial soils vary from "soil-less" blends of peat moss/perlite mixtures that contain no actual dirt material to specific blends of the right nutrients and ingredients for different types of plants or container needs. Basic potting soil, though, will contain enough nutrients for most plants for the planting season. Know that potting soils are meant to be a temporary medium; always use new potting soil each time you plant to ensure the proper amount of nutrients.
Nitrogen is the most abundantly used nutrient by plants. A key component in the formation of chlorophyll, nitrogen makes plants green, thus allowing it to create the food the plant needs to grow. One of the reasons container-grown plants can grow so much larger than the same plants in the flower bed is the fact that container plants do not compete with anything else for the nitrogen in the soil. Nitrogen is used quickly by growing plants, so even when using a premium potting medium, it is best to provide a regular shot of fertilizer or compost tea to keep the nitrogen levels up. If potted plants show signs of yellowing in the leaves or stalk prematurely, then they are showing a lack of nitrogen and need more fertilizing.
Potassium provides all living creatures with cell-building components. Sometimes known as potash in gardening, potassium helps build strong stalks. Potassium is added in a lower dosage than nitrogen as it is slower used and should not have to be added to container plants except through a liquid fertilizer.
Phosphorus is a mineral that builds strong root systems and is needed for seed production. While most container-grown plants are annuals and usually not coveted for their seed production, flowers that are actively seeking to produce seed must produce more blooms to achieve the seeding stage.
Trace Minerals and Other Ingredients
Potting soils are often a mixture of sphagnum moss, peat, perlite or vermiculite, composted bark and other trace minerals needed for healthy plants. The sphagnum moss and peat make for a lightweight, airy mixture that allows for easy root expansion and easy drainage. Perlite and/or vermiculite help with water retention, proper drainage, and prevents the mixture from hardening. Compost helps give the soil composition and provides many of the above-mentioned nutrients as well as trace minerals such as magnesium, calcium, sulfur and carbon, all needed in small doses.